Indicating and recording systems



R. c. RAYMOND 2,648,838

INDICATING AND RECORDING SYSTEMS Aug. 11, 1953 Filed July 27, 1949 6 Sheets-Sheet l Aug. 11, 1953 Filed July 27, 1949 R. C, RYMOND INDICATING. AND RECORDING SYSTEMS 6 snags-sheet 2 ATTORNEYS I l Aug. 11, 1953 R. c. RAYMOND 2,648,838

INDICATING AND RECORDING SYSTEMS F'iled July 27, 1Q49 6 Sheets-Sheet 3 G' ene/*a fr Terra/r1 I Aug. 11, 1953 R. c. RAYMOND NDIcATING AND RECORDING SYSTEMS Filed July 27, 1949 nn l 1 1 l l l ||.I

IN VEN TOR.

Aug. 11', 1953 R. c. RAYMOND 2,648,838

INDICATING AND RECORDING SYSTEMS VFiled July 27, 1949 e sheets-sheet 5 6. 7 INVENTOR Richard C. Haz/mand Aug. 11, 1953 R. c. RAYMOND 2,648,838

INDICATING AND RECORDING SYSTEMS 4 Filed July 27 1949 6 Sheets-Shet 6 lenses Z E5 ens 'QL AMP ANP - vfTae 22/ INVENTOR. 2224 Frfc/vara' C. Raymond I f a? ATTORNEY` Patented Aug. 11, 1953 UNrrEo INDICATING AND RECORDING SYSTEMS Application July 27, 1949, Serial No. 107,005

21 Claims.

This invention relates to indicating and recording systems and has for its primary object the provisions of means for indicating and/or printing the output of a radar set in an improved manner. A more specific object is to provide a system adapted to be used aboard an aircraft for printing contour lines. Various other objects and advantages will appear as this description proceeds.

One of the specic forms of the invention herein described contemplates a device for use aboard an aircraft for printing a map of the terrain and also for printing another map the only indicia on which consist of contour lines. The apparatus employed aboard the aircraft includes a radar set and two printersvone of which prints `a map according Vto the output of the radar set. The other printer is a contour line printer and is responsive to the output of the radar set. It has an` input circuit that feeds impulses thereto only when the impulses correspond to contour lines. If desired the input circuit to the contour printer can be modified by a barometric altimeter to correct for Variations in the altitude of the aircraft. Other means are employed to correct for Variations in the angular position of the aircraft.

A detailed description follows, and the novel features are set forthY in the appended claims.

In the drawings:

Figure 1 is a diagram useful in explaining the Y invention.

Figure 2 is a schematic block diagram of one form of the invention, the printers being shown in perspective.

Figure 3 is a diagram illustrating the problems involved in correcting the system for variations in the angle of the aircraft.

Figure 4 is a schematic diagram of the circuit for correcting for variations in the angle of the aircraft.

Figure 5 is a schematic diagram, with the printers shown in perspective, of a modified form of the invention.

Figure 6 is a Schematic diagram of the radius computer of Figure 2.

Figure 7 is a schematic diagram of the elevation computer of Figure 2.

Figure 8 shows the voltage output of the scale of 8 circuit of Figure 7.

Figure 9 is a block diagram of another form of my invention involving color printing.

Figure 10 is a schematic diagram of sweep generator 222 of Figures 4 and 9. Sweep generator 208 is of similar construction.

Although the possession of accurate contour or relief maps of a terrain region is of great importance in such operations as military campaigns, airV navigation, highway planning, agriculture, and many other activities, there are at present large areas of the earth which have not been mapped in a way which provides knowledge of the elevations of the terrain at various points, because of the enormous labor involved in making the necessarily large number of individual terrain observations and computing and plotting the necessary maps. The system to be described below is a complete unit for the taking and recording of several thousand terrain observations each second and the plotting of these observations in the form of a contour map which is familiar to persons skilled in mapping and in the use of maps. The device also provides for a recording of the radar reflectance of the various terrain elements which come under its observation so that the contour map may be keyed in with water courses, cities, bridges, and other prominent radar reiiectors to couple it with eX- isting'fmaps and with other maps made by this same process.

The terrain observation is performed from an aircraft by means of a radar system which periodically sends out short pulses of high frequency radio waves to travel to the terrain and back along the direction of a fairly well defined beam of radiation. The system of computation of the contour map elements from the radar information can best be understood by an examination of Figure l. This ligure shows the radar bearing aircraft in ight along line E at altitude h over base plane 3. The radar beam radiated from the aircraft at angle 0 below the horizontal is represented by zone 4. The radar pulses sent out along beam 4 intersect terrain profile 5 in a small segment 6 and a portion of the radio frequency energy is re-radiated or reflected from terrain element 6 to the radar set in the aircraft. l Measurement of the time interval at the aircraft between the radiation of a pulse and the receipt of its echo may be used to determine distance R, as the radio waves propagate through air at the Welll known velocity of 186,000 miles per second. At the same time, knowledge of altitude h through the operation of a sensitive barometric altimeter and knowledge of angle 0 permit the calculation of distance R0, which is the distance the waves would have travelled before reflection to reach base level 3. Rotation of the radar antenna about vertical axis 2 allows the determination of R for terrain elements lying on .g ef) a rough circle about the point of intersection of line 2 with the terrain. As the aircraft progresses along line I, the mapper sweeps out a zone whose Width is approximately 2r. For each observation, the radar set in the aircraft determines R, 0, and qu, Where e is the angle of rotation of the radar antenna about axis 2 with respect to the central axis of the aircraft, or with respect to magnetic North, depending on the coordinates which are chosen.

The computations which are of interest in reducing the above data to map form involve the determination of r and the determination of A for a given set of values of rp, 6, and R and a measured value of h. These calculations are formed in the following way:

1*:R cos 0 1 A= RR sin 0 2 Ro=h,/ sin 3 Combining Equations 2 and 3 We have A=hR sin 0 4 The map printer to be hereinafter described forms signals dependent on the computed value of A and prints them on paper at scale distances r and angles p from the scale positions of the aircraft. Since the scanning motion of the radar antenna may cause information to be drawn from contiguous or overlapping terrain elements,

the elevation symbols on the map may be the tenna array |0I capable of projecting energy into narrow beam 4, and a receiver IUE sensitive to the weak echo signals returned from terrain element 6, as received through antenna |0I. Pulser IOF supplies very short trigger pulses to the radar transmitter IIlC and to cable |02 as 'is well known.

Cable |02 from radar set I0 carries the trigger pulses which are respectively timed to coincide with the transmitted pulses of radio frequency energy from radar set I0. Each trigger pulse is carried to radius computer I2 and to elevation computer II where it serves to start the cycle of computation of the correct radius of terrain element 6 and the elevation of terrain element 6 above the previously chosen base level.

Cable |03 carries the returned echo signal from terrain element 6 to elevation computer I I and to selector I4. The time elapsed between the trigger pulse on cable |02 and the returned terrain signal on cable |03 is used in computers I I and I2 for the computation of the correct printing radius and the correct elevation signal.

The operation of elevation computer II is controlled and corrected by altimeter I8 for changes in the altitude of flight of the aircraft, but in the first form of the system herein illustrated other fluctuations in the aircraft flight path are uncorrected and may introduce distortions in the map. A second form to be described later has provision for certain corrections to eliminate the effect of aircraft fluctuations.

Printer I produces a contour map, on which marks are made in the form of contour lines to indicate the elevations of terrain points from which information is received. Printer I6 produces a map which is geometrically to the same scale as that of printer I5, but in which a signal is printed continuously which is dependent on the amplitude of the returned echo signal. The printers contemplatedY here are of the facsimile type, in which an electrical impulse passes through a paper which is sensitized by chemical means and causes a change in the color or light reflecting power of the paper. It would also be feasible to use other recording means, and in printer I5 it would be possible to print a density7 corresponding to the elevation of the terrain elements instead of printing ordinary contour lines.

The synchronous motors I1, ITA and IOA which respectively drive the roller |54, roller |54A, and shaft IOB, operate at the same speed and are energized by the same alternating current power leads |04.

Printers I5 and |6 are similar in mechanical form and differ only in excitation. Printer I5 is shown in Figure 2, and its operation will be understood to be the same as that of printer I 6 except for the nature of the electrical signals which are passed to it for printing. Printing paper is drawn from supply roll |5| by drive unit I 53 which actuates rollers |55 to pull the paper from roll I5I through the printing assembly at a speed proportional to the ground speed of the aircraft. The printing is done between cone |54 and plate |52. Cone |54 is driven by motor I 'I in a circular path over plate |52, and the printing is ,accomplished by the passage of electrical current between cone |54 and one of the conducting rings which make up plate |52. The projection of the vertical shaft of unit I1 onto the paper is the scale ground position of the aircraft, and the angle of cone |54 about this shaft is maintained synchronously with the angle of the radar antenna about its vertical axis by drive unit IOA. Selector I3, operating in response to range computer I2 picks the ring of plate |52 which represents the scale radius of the terrain element being printed, and the signal representative of altitude as determined by computer I I is applied to the selected ring. In this way, every time the radar beam passes the position of a contour line on the terrain, a mark corresponding to the contour line is drawn in scale position on the map by printer I5. The result, after a period of flight is a contour map with lines |56 indicating the elevations of the terrain elements which come under the observation of the radar set. The way in which these signals are derived will now be explained.

Radius computer I2 is illustrated in detail in Figure 6. It receives the trigger pulse from radar set I0 and supplies signals to selectors I4 and I3 dependent on the printing radius. The printing radius is broken up into discrete incremental elements as shown in Figure 2 by the use of discrete range rings in plate |52. Computer I2 divides the time after transmission of the radar pulse into a number of discrete intervals corresponding with the rings in plate |52 and passes information on this selection to selectors I3 and I4. Referring to Figure 2, the trigger pulse from radar set I Il operates through reset element |22 to stop the action of oscillator |23, clear scaling circuit |24, and stop the action of counting elements |25 through |29. A short time later the same trigger pulse passes through delay circuit |2| and serves to start the operation of the computer for the new radar pulse. Oscillator |23 is started by the pulse. It sends periodic impulses to scaling circuit |24 and to counting elements through |29. Scaling circuit v|24 receives the pulses until it has counted a number corresponding to the radius of the innermost printing ring of plate 52 (hereinafter called the IR number) and then passes a pulse to counting element |25. Element |25 cannot respond to pulses from oscillator |23 until it receives a pulse from scaling circuit |24, but after receipt of both pulses it passes a signal to element |26, which on receipt of the next impulse from oscillator |23 passes a signal to element |21. Elements |25 through |29 are thus energized in successive order, returning to their quiescent states after passing signals to the succeeding elements. Although only five elements are shown here for purposes of illustration I actually employ a large number of such elements one for each of the large number of rings in plate |52.

The frequency of oscillator 23 is determined by the range interval between rings on plate |52 and by the angle e by which the radar beam is depressed below the horizontal. Specifically the frequency of oscillator |23 is given by f=e cos e/2dr 5 where f is the oscillator frequency, c is the velocity of radio Waves, and dr is the difference in radius along the ground presented by the spacing between adjacent rings of printing plate |52. Scaling circuit |24 counts a number of pulses called the IR number:

where n is the IR number of pulses and To is the radius of the innermost ring of plate |52. Each of elements |25 through |29 corresponds to an individual ring in plate |52. The signals passed from computer l2 to selectors |3 and I4 thus enable printing with successive rings of plate |52 as determined by the time after transmission of the radar pulse, the values of cos 9 and dr, and the radius of the innermost printer ring, ro.

In Figure 6, which shows the radius computer |2 in greater detail, the radar trigger pulse is received over wire |52 and any direct current components are blocked by condenser IAI, and this condenser in combination with resistor |A2 serves as a diiferentiating device to produce a steep positive voltage spike at the beginning of the radar trigger pulse and a steep negative voltage Yspike at the end of the radar trigger pulse. Diode vacuum tube |A4 does not draw current on the positive spike, but does draw current on the negative spike and serves in conjunction with resistor IAS to prevent the large negative spike from reaching the grid of tube IA5. Resistor :IAG and condenser IA'! serve to bias tube IAE in the conventional way, and the sharp positive voltage spike causes increased electron current in tube |A5, which increased current flowing through resistor IAQ and inductor IAS causes a sharp negative output voltage pulse which is passed out through condenser IAIB to actuate the oscillator |23, and counting circuits |25 to |29, etc., through tube |A|2. Tube |A|2 is used as a phase inverter to supply positive pulses to those circuits requiring a positive reset pulse.

Oscillator |23 which is diagrammed in Figure 6 is a common type of radio oscillator with an output stage designed to produce a series of evenly spaced negative pulses. It is turned oi by negative reset pulses (which block the grid of 2A5) and started again by the positive radar trigger pulse passed through delay circuit |2| through the action of tubes 2A5 and 2Al3. These tubes 2A5 and 2A|3 serve to place a negative grid bias on oscillator tube ZAI'I during the period of quiescense. Tubes 2A5 and 2A|3 form a more or less conventional flip-flop circuit of the multivibrator type. Tube 2A5 is normally conducting and tube 2A|3 is normally biased beyond cutoff by current owing through resistors 2A|2 and 2A9. When the negative reset pulse is applied to the grid of tube 2A5, the multivibrator action-reduces the current in tube 2A5 to zero and causes current to flow in tube 2A|3. This results in a decrease in the plate voltage of tube 2A|3 which is communicated through condenser 2A|4 to the grid of tube 2Al1, causing the grid to be biased far beyond cutoff and causing oscillations to cease. Delay circuit 2| is comprised of a number of series inductive elements and parallel capacitors which represent a long section of electrical transmission line and thus delay the trigger pulse by an amount of time suicient to permit resetting of the remaining circuit for a new computation. When the radar trigger pulse arrives through delay circuit |2|, it reverses the phase of operation of the multivibrator, causing the plate voltage of tube 2A|3 to rise sharply and bringing the grid of oscillator 2A|`| back into the operating region. The frequency of oscillator 2A|1 is controlled by tuned circuit 2A223 and by the action of reactance tube 2A25. Tube 2A25 is excited from the oscillati-ons in tuned circuit 2A20. Condenser 2A26 and resistor 2A2'I shift the phase of grid excitation so that the alternating component of plate current flowing in tube 2A25 is in a reactive phase relationship with the plate voltage. The amount of reactance can thus be controlled by the grid bias of the tube. 'I'his grid bias is derived from the correction circuit of Figure 4, and as hereinafter explained serves to change the frequency of oscillator |23 in accordance with angular displacements of the aircraft. In the simple system, uncorrected for aircraft motion, tube 2A25 is omitted. Tube 2A23 is biased to cutoff. An exciting coil in its grid circuit is coupled to tuned circuit 2A20. The tube output thus consists of a series of negative voltage pulses which are spaced evenly at the frequency of oscillation of the circuit of tube 2A| 7. These pulses are passed on to operate the remaining units.

As will be apparent, scaler |24 is essentially a counting circuit which counts a number of output oscillator pulses dependent on the scale diameter of the innermost concentric ring of printers I5 and I6. Since the oscillator starts to operate shortly after the emission of each radar pulse and the innermost printer ring is not at zero radius, it is necessary to count a number of oscillator pulses before starting the operation of stepping circuits |25 through |29. This might alternately be done by increasing the delay of circuit |2| and omitting sealer |24, but the sealer is preferred for reasons of flexibility and reliability. Scaler |213 includes a number of similar units the rst unit of which is shown in detail in Figure 6. The first of such units consists of parts 3A| to and inclusive of SAIS. 'Iwo other such units are shown in block form and bear reference numbers |25B and |2-4C. It is of course understood that While I have shown only three units, I contemplate a larger number of such units as making up sealer |24, all of which will hereinafter appear and become obvious. Each unit serves to divide the number of input pulses by two so that the use of a number of such units in series will count readily numbers of' pulses which are simple powers of 2, such as, 2, 4, 8, 16, 32, 64, etc.A The counting of 4096: pulses, for instance would require a cascade of l2 units. If intermediate numbers of pulses are required they can be obtained by the use of interpolation circuits based on the currents flowing in the various units of the scaling circuitA or by the use of subsidiary scalers actuated at the completion of a predetermined count by this circuit. The circuit of sca-ler IM is merely one type of sealer which could be used, and many similar ones are known in the art (see for example Cork, Radioactivity and Nuclear Physics, D. Van Ncstrand (New York) 1947, p. 45)

The sealer |24 of Figure 6 receives the train of negative pulses emitted by the oscillator or a divided train of negative pulses emitted by a previous similar unit, according to its place in the scaling chain. The negative pulses are passed by diode tube SAI to the first grids of both tubes 3A2` and 3A3. The circuit formed by tubes 3A2 and 3A3 is a feedback amplier type of circuit sol arranged that it has two stable conditions and so that successive pulses received on the first grids of the tubes will flip it alternately from one stable position to the other. In the conditionobtaining after operation of the reset Y circuit, tube 3A2 is conducting a large electron current, causing its plate voltage to be rela- 7 tively low. This low voltage is communicated through resistor 3A@ to the second grid of tube 3A3, where in combination with a negative voltage applied through resistor SAI I, the o eration of the second grid of tube current in that tube and permit the plate to assume a relatively high voltage. This high voltage is communicated in turn through resistor SAQ to the second grid of tube 3A2, where it prevents the resistor ,"EAIO from cutting off the grid and thus maintains the flow of current in the tube. When a negative pulse is applied to both grids it can have no eifect on tube @A3 since plate current is already cut oif, but it diminishes the current through tube 3A2, causing the potential of the plate to rise and causing a sharp rise in potential of the second grid of tube SAB. Plate current in tube 3A3 is started by the rise in grid voltage. This serves to diminish the voltage of the plate of tube BAS and in turn to diminish the voltage of the second grid of tube 3A2 to the point where plate current is cut off in tube 3A2 and the circuit has been transferred to its alternative stable position. A second negative pulse applied to both grids through diode SAI fails to affect tube 3A2 but reduces the current in tube 3A3 and so shifts the circuit to its original condition.

Output from the circuit is obtained through condenser SAIS which feeds resistor 3A|1 and diode SAQ. During the first change of phase of the circuit, the pulse reaching diode 3A4 is positive, caused by a cutoff of plate current of tube 3A2, and is therefore not transmitted to the next circuit. During the return to original condition, caused by the second pulse, diode 3A4 passes the resulting negative pulse to the next circuit. Diodes SAI and SAB are similar in function, and only one of them is needed between circuits. lIhe circuits IMB, |240, etc. may omit tube 3AI and may be therefore composed of only three of the four tubes shown.

Resetting of the circuit is accomplished at the completion of a pulse interval by a positive pulse 3A3 is to cut off plate negative voltage applied through 8 applied through condenser SAIS to theV second grid of tube 3A2. This reset pulse does not affect the circuit if tube 3A?. is conducting but renders tube 3A2 conducting and tube 3A3- nonconducting if the circuit is not already in that condition.

Stepping circuits |25 through |29 are similar indesign and in purpose. It is the intent ofthe stepping chain to take an output pulse at the conclusion of operation of scaler |24 and pass an active pulse along the line, moving the active stage one step for each negative output pulse from oscillator |23. The several Steppers |25 to |29 inclusive are all of similar construction and therefore Figure 6 illustrates only the rst of them in detail. Their output leads IZEX to IZBX respectively pass to the selectors I3 and I4 as shown in Figure 2. Tubes AAI and A2 are. connected in a one shot multivibrator typeof circuit, involving regenerative feedback. vTube II'AI is normally maintained at a grid voltage beyond cutoff by current owing through resistors 4AI4 and IIAIZ, It is thus normally insensitive to the oscillator pulses applied through condenser A'I. At the conclusion of scaler activity, or at the termination of the open time of the previous stepper circuit, if this is not the first one in the chain, a positive pulse is applied through condenser iAt to the grid of tube AQAZ. The pulse is of sufcient ampliture to start the ow of plate current in tube @A2 and through the regenerative feedback action of the circuit, tube IEAZ is soon fully conducting, and tube IIAI is nearly cut off. The start of plate current in tube @A2 passes a negative pulse from its plate to the next stage through the output lead, but since the tube to which it goes is biased beyond cutoff, no passing of the pulse results. When the next negative oscillator pulse reaches the grid of tube AZ, the multivibrator action is reversed, and tube liA2 is once more cut oif and 4`AI rendered conducting. The positive pulse generated at the plate of tube IIA2 by the reversal of the multivibrator starts the action of the next stepping circuit. In the quiescent state of the circuit, the Voltage of the plate of tube AAI is relatively low, because of current conducted through resistor A8, During the timev of operation of this stepper, the current of tube EAI is reduced and the plate voltage thus rises. Condenser `IAS is used to communicate this rise in voltage to selector circuits as shown in Figure 2.

The reset function to make the stepping chain ready for the next pulse is carried out by a posi.- tive pulse applied to the grid of tube 4Al. If the circuit is already in its quiescent state, no further action occurs, but if it is in the active state it is vreturned to the quiescent state by the action of the reset pulse.

Figures 2 and '7 illustrate the action of elevation computer I It is designed to start a.. cycle of operation on receipt of the trigger pulse and to deliver the selector I3 a signal whose intensity or other characteristic may be dependent on the elevation of the terrain element above the base level. In the form of instrument described here, the printing of contour lines is contemplated, and the signal passed to the printer is modiiied by computer II so that a number of separate intensity levels dependent on the elevation are repeated in succession in the same way that the weight of contour lines on an ordinary map is varied in cyclic fashion.

The trigger pulse received over cable |02 from radar setv I0 is passed into delay circuit H10 and 9. to reset circuit III. The latter stops the action of oscillator H2 and resets scaling circuit H3 to a position determined by the reading of altimeter I8. The trigger pulse arriving through delay circuit H starts oscillator H2. Oscillator H2 passes successive electrical impulses to scalingcircuit I I3, which alters its condition in cyclic fashion, starting with the condition determined by altimeter I8 and passing through 8 successive conditions before repeating.

The video signal return from radar set Ill passes along wire ID3 and is applied as it is received to pulse former H6. This circuit determines the center of the rising edge of the return pulse and forms a pulse at the instant and independent of theamplitude of the radar return pulse. The pulse formed from the radar return is passed through circuit H5 where it is examined for coincidence in time with a portion of the output impulse of oscillator H2. Pulses from forming circuit H6 which are coincident with those from oscillator H2 are then passed to modulator H4. Those which are not coincident within certain limits are rejected by coincidence circuit II5. In modulator H4, the pulses passed by coincidence circuit I I5 are modulated in amplitude according to the condition of scaling circuit H3 and passed to the selector stages for printing. The output to the selector stage thus occurs when the radar return pulse is essentially coincident with a cycle of oscillator H2., orcoincident in elevation with one of the established contour intervals. This output is modied by modulator H4 to show which contour line is involved, as determined by scaling circuit H3.

, Referring to Figure '7, which shows the elevation computer I I in detail, it is noted that reset circuit I I I is generally similar to reset I22 of Figure 6, and like parts bear like reference characters except that those of Figure 7 are primed. Likewise, oscillator H2 of Figure 7 is similar to oscillator I 23 of Figure 6 and like parts bear like reference characters except that those of Figure 7 are primed. Pulse forming circuit H6 is for the purpose of preparing the radar ground return pulse for use in coincidence circuit I I5. Coincidence circuit H5 determines Whether the radar return pulse coincidences in time with one of the negative pulses from oscillator H2 in order to determine whether a contour line should be printed for that particular return. Scale of 8, H3, and modulator H4 determine the density of the contour line which is printed in response to the signal passed by coincidence circuit I I5.

Figure 7 also illustrates the cooperation of a1- timeter I8 with reset III. Tubes 5AI through 5A8 comprise the scaling circuit. This circuit is similar in function to the circuit of Scaler.

|24 of Figure 6 but differs in a number of details. Tubes 5AI and 5A2 constitute one element of the circuit, and their operations are essen-v tially duplicated by those of the remaining two pairs of tubes. Tubes 5AI and 5A8 are diodes which serve to couple the circuits in such away that only negative pulses may be passed'from circuit to circuit. As will be seen in the gure. the feedback connection in each scaling pair is made by connecting the suppressor grid of each pentode to the plate of the opposite tube. The cathodes of the two tubes are also connected in parallel across the same cathode resistor so that if one of the tubes is conducting and the other lone is non-conducting the condition will remain that Way by virtue of the cathode bias connected CII from the conducting tube to the nonconducting one and the fact that the suppressor grid of the conducting tube is maintained at a relatively high voltage by the lack of plate current in the nonconducting tube and the suppressor grid of the nonconducting tube is maintained at a relatively low voltage because of the voltage drop in the plate resistor of the conducting tube. Under these conditions, a negative pulse applied to both grids in parallel will serve to reverse the condition of the scaling circuit in much the same way described in the case of scaling circuit I24, and as scaling circuit H3 is connected, every second pulse will bev transmitted to the second pair of tubes, every fourth to the last pair, and every eighth will return the entire circuit to its original conditions. If we connect resistors such as 5A9 and EAII) into one plate lead of every pair and proportion their resistance values so that vthe contribution from the second pair is about twice and that of the third pair about four times the contribution of the first pair to the output circuit, the lead I I IX to modulator I I4 will carry a positive voltage which decreases by regular steps for each oscillator pulse until it has gone down seven steps and then returns to its original value at the eighth pulse, as shown in the graph of voltage as a function of time in Figure 8. This regularly changing voltage is used in modulator H4 to determine the density of contour lines to be printed according to the terrain elevation from which the echoes are received.

It is obvious from the foregoing that tube 5A5 and the resistors in series With it are designed to carry a heavy current. The resistors 5C9, 5CI and 5CH are selected of such value as compared to the others in the scale of 8 circuit that vvhen tube 5A5 is conducting and 5AI and 5A3 are not conducting that the potential on wire IIIX will drop to half of the potential it would attain if none of tubes 5AI, 5A3 and 5A5 were energized. It is noted in this connection that there are two current paths from battery 5B to the anode of tube 5A5. One of the paths is through resistors 5CIO and 5C9. The other is through resistors 5AIO, 5AI2, 5CI I, and 509. The current in the anode of tube 5A3 is less than that for tube 5A5, and resistors 5B9, EBI!) and 5BI2 have such resistance values in relation to the others in the circuit that tube 5A3 when energized will cause the potential on Wire IIIX to drop about one half as much as tube 5A5 causes it to drop. Similarly resistors 5A9, 5AIII, and 5AI2 are of such values that when tube 5AI is energized that it will cause the potential on Wire IIIX to drop about half as much as when tube 5A3 is energized. The relationships of the values of all of the resistors referred to in this paragraph are such that if none of tubes 5AI, 5A3 and 5A5 are energized the potential on line IIIX will rise to a given value which I will call 8 units of potential. When tube 5AI is energized (5A3 and 5A5, not being energized)- the potential onA IIIX is seven units. If 5A3 is energized (5AI and 5A5 not being energized) the potential at IIIX is six units. When 5AI and 5A3 are energized (5A5 not being energized) the potential at IIIX is 5 units. gized (5AI and 5A3 not being energized) the potential at IIIX is four units. When 5AI and 5A5 are energized, and 5A3 not energized, the potential at IIIX is three units. If 5A5 and 5A3 are energized, with 5AI not energized, the potential at IIIX is two units. With all three of 1l AI, 5A3 and 5A5 energized the potential at II IX is only one unit.

Resetting of the scaling circuit is carried out with reference to the pressure altitude of the aircraft so that variations in the aircraft altitude during a mapping flight may be corrected for automatically in the nal printing. Negative pulses from reset III are passed through commutator 5AI2 to the reset leads from scaling circuit II3. Barometric altimeter I8 which is shown schematically moves the commutator bar 5AI2I so that it engages segments appropriate to the aircraft altitude above the datum level. The top row of segments (which includes lsegment 5AI3) is connected to the first scaling pair of tubes 5A! and 5A2 and is composed of relatively short segments. The rst scaling pair is therefore reset to a condition dependent on small changes in altitude. Each segment of the second row of segments (the row including segment 5AI4) corresponds to twice the change in altitude of the first pair, and each segment of the third row of segments (the row including segment 5AI5) corresponds to four times the change in altitude of the first pair. In each row alternate segments are connected through appropriate resistive networks to alternate grids so that the negative reset pulse is passed to one grid or the other, depending on the condition to which it is desired to reset the scaling pair. The segments in the first row correspond in altitude to the difference in altitude between adjacent contour lines so that proper modulating voltages are supplied to the map printer, independent of the aircraft altitude. It is of course understood that addition of more tubes and more commutator contacts would make it possible to use more than 8 different levels of voltage, or conversely that some of these levels may be omitted by proper redesign of the equipment. The number 8 is chosen as representative of a desirable number in practice.

Figure 7 also illustrates pulse former IIB, coincidence circuit I5, and modulator 'l I4. Tubes EAI and 6A2 are coupled in a one shot multivibrator circuit designed to receive the radar ground return signal and produce from it a wave of essentially rectangular form whose amplitude and duration are independent of the form of the return signal. In operation tube SAI is normally biased to cutoff through the action of resistors GAS and BA1. The positive pulse received from the radar receiver is differentiated somewhat by condenser 6A9 and resistor GAI!) and the leading edge of the pulse is applied to the grid of GAI. The multivibrator action causes tube SAI to conduct and cuts off tube 6A2 for a period determined by the constants of the multivibrator circuit, producing a rectangular wave of voltage of positive sign at the plate of tube 6A2. The rectangular Wave is diiferentiated strongly by condenser GAII and resistor 6AI2 'and applied to the grid of tube GA3, which operates as a cathode follower with a plate current approaching a saturation value. lThe positive voltage spike resulting from the differentiation of the rectangular wave has little effect on the plate current of tube GA3, but the negative spike is passed due to the non-linear operation of the tube. Tube 6A4 operates as a coincidence amplifier. It is adjusted to give little output when either of its grids is excited separately but to 1&2 give a full positive pulse output when both grids are pulsed negatively at the same instant. One grid is driven by the wave described above, developed from the radar terrain return, and the other grid is driven by the regular pulses of oscillator II2. When the radar return pulse is essentially coincident with a pulse of oscillator H2, it means that the terrain echo comes from a point which is at or near the elevation of one of the selected contour intervals, and a pulse is passed to the injection grid of tube 6A5. In tube BAS, the pulse passed by tube 6A!! is modulated by the signal from sealer IIS to indicate which of several contour intervals is involved, and the output signal of tube GAS is passed over Wire IMX (see Figures 2 and 7) to the selector circuit I3.

The operation of Figure '7 can be illustrated by studying a specific example of operation as follows: Assume that when the aircraft flies at 7000 feet above base level 3 (of Figure l) that the contactor JAIEI engages contact strips 5AI3, SAM and 5AI5. Assume further that for each 1000 feet that the aircraft descends that contactor EAIZI moves to the right by one contact element, hence when the aircraft is at 6000 feet the contactor 5AI 2l will engage contact elements SAIS, 5AI4, and 5AI5. When the aircraft descends to 3000 feet, for example, the contactor 5Ai2| will engage contact elements SAIT, 5AI8 and 5AI 9.

Reverting back to the assumptions applying to '7000 feet it is noted that when a pulse is received from the radar pulser over wire line |02 the pulse will pass through reset I'II to the contactor EAIZI, and therefrom to contact elements 5Al3, 5AI4, and 5AI5. These contact elements are respectively connected to the grids of tubes EAI, 5A3 and SAE. Since the pulse applied to contactor 5AI2I is negative these three tubes are all biased to cut-off. Under these circumstances no current iows in any of resistors 5AI D, 5BIO or 5CH), and therefore substantially the full potential of battery 5B is impressed on wire I'IIX, however there is some resistance in the circuit and therefore I will assume that this condition of the apparatus represents 8 units of potential applied to the grid 6AM. 'Io illustrate further the following table shows whether the several tubes are conducting (represented by C) or non-conducting (represented by N), for the eight different conditions prevailing in response to the receipt of seven pulses:

Number of pulses Units from oscillator 5A1 5A2 5A3 5A4 5A5 SAG of Potential N N C N C 7 C C N N C 6 N C N N C 5 C N C C N 4 N N C C N 3 C C N C N 2 N C N C N 1 C N C N C 8 In studying the foregoing table it is noted 'that when tube SAB is conducting it reduces the potential by four units, when 5A3 is `conducting it reduces the potential by two units, and when 5AI is conducting it reduces the potential by one unit.

Let us now assume that the aircraft descends to 6000 feet and contactor 5AI2I moves to con- 13 tact element 5AI6. The table for this condition is as follows:

Assume that the aircraft descends to 3000 feet, the contactor 5AI2I would move to contact elements 5AI1, 5AI8, and SAI 9, and the table would appear as follows:

Number of pulses Units from oscillator 5Al 5A2 5A3 5A4 5A5 SAG o1' Potential N C C N C N 2 C N C N C N 1 N C N C N C 8 C N N C N C 7 N C C N N C 6 C N C N N C 5 N C N C C N 4 C N N C C N 3 N C C N C N 2 It is further noted that the first row of contact elements (the row including 5AI3 and 5AI1) may include more than seven elements, even though there are only eight different units of potential available. In event the contactor 5A|2I advances past the seventh contact element 5A20, the Value -of potential representing that altitude will be the same as the value that represents an altitude eight contact elements higher.

The selector I4 has ampliers I3IA to I35A which are identical to amplifiers I3I to |35 respectively, and the parts of terrain printer corresponds to parts of the contour printer bearing similar reference numbers, however parts of the terrain lprinter include A on the end of their reference characters.

To further illustrate the operation of the system, assume that the aircraft is flying at 6000 feet and that the radar beam il intercepts an element 5 (see Figure 1) which is at 5000 feet. The pulser IDF transmits the outgoing pulse to the transmitter IGC, reset |22, delay circuit I2I, reset III, and delay circuit III). The altimeter I8 has moved the contactor 5A|2I to engage contact elements 5AI6, SAIE and 5AI5. Then the pulse over line |02 biases tubes 5A2, 5A3 and 5A5 to cut-off. The two delay circuits delay the pulse for a short period. At the termination of that period, oscillators II2 and |23 begin to generate pulses. Since the elevation of the craft above ground element 6- is not great, only a few pulses will be generated by oscillator |23 before there is a return pulse detected by receiver IUE and passed along to Wire |53. Assume that the return pulse corresponds to the third pulse from oscillator |23, then pulser element |21 and amplii'lers |33 and I33A will be energized concurrently with the return pulse on line |53. These amplifiers will not, however, energize their complementary rings of the printers unless their second grids are energized. The return pulse on line |63 energizes the second grid of amplier I33A concurrently with the energization of amplifier I33A by element |21, and therefore a pulsepasses` to the third ringof printer I6.

The intensity of the printed spot will dependv on the ability of element 6 to reflect, and also to some extent on the altitude of element 6. However in the determination `of the altitude of part 5, the contour map which has only contour lines, is laid on top of the terrain map. When said return pulse passed over line |03 it energized pulse former H6, and coincidence circuit II5. The output of the coincidence circuit energizes modulator |Ifl. Concurrently the oscillator |23 'would generate its first pulse and thus trigger scale of 8 to reduce its output potential by one unit from its 8 unit of potential condition. Thereforey the amplitude of modulation impressed on wire IIIX will be M; of maximum. This output will loe concurrent with the energization of the rst grid of amplier |33 by element |21.

The output of amplifier |33 is stored to somedegree in condenser I33C to broaden the pulse,

and is then applied to the third ring of contour.

'" printer I5.

The roller |54 prints the pulse at an angular position correspon-ding to the angular position of antenna IUI. It is noted that only elements of terrain falling within a specined tolerance near contour lines will be printed. This results from the fact that coincidence circuit |I5 only passes pulses when they are nearly concurrent with one of the pulses from oscillator i I2. This oscillator generates pulses correspondy l ing to the levels of the several contour lines.

Certain of the features of the two printers I5 and I t herein shown, and their relation to other parts of the circuit are described in my prior copending application Serial No. 92,616, filed Y Ivi-ay 11, 1949, entitled Method of and Apparatus for Indicating and/or Recording Data, now abandoned.

Selectors I3 and I d are identical in construction and similar in function. Each one consists of a number of amplifier stages which are controlled by the output of radius computer I2 so that only one amplifier is energized at any instant during the printing cycle. These amplifiers serve to select the printing rings in the base plates of printers I5 and I6 corresponding to the proper scale radius and to pass the printing signals derived from elevation computer II to printer I5 and from the radar video return to printer I6. They also serve to lengthen the time interval occupied by the signals underv discussion so that more time may be taken to print,

the signals properly on the facsimile paper.

Since the two selectors are identical, only selector I 3 will be described in detail.

Radius computer I2 produces a sign-a1 on onel to a particular scale radius -on the printed mapl from the vertically projected position of the aircraft. Amplifier stages |3I through |35 are all similar, and amplier |35 is shown in `detail as a conventional amplifier. The output of elevation computer 'II is applied to all the stages in parallel, but unless the output of radius computer I2 is applied simultaneously, no voltages are delivered to printer I5. When the output of computer I I coincides with the output of computer I2 in a particular amplifier stage, that stage produces an output which is printed by the apr' propriate.. ring-of printer I 5.Y -In operation, a

15 nite vtimev interval occurs between the transmittedradar pulse and the excitation of amplifier |3|. After a time corresponding to the radius vof the innermost printing ring in printer |5, amplifier ISI is enabled. After a further short interval, corresponding to the range difference between the first two rings, amplifier |3| .is vblanked and amplifier |32 is enabled. The succession of pulses produced by computer l2 proceeds up the chain, enabling the amplifiers one at a time, in order. The signal from computer `|S| is thus amplified by the stage corresponding .to its proper ground range and printed by the proper lring of printer |5.

It is obvious that the production of undistorted maps by 'the instrument described above requires that .the aircraft ily a reasonably level course in one direction and that it avoid errors in pitch, yaw, and roll, or that its antenna system be stabilized against rotation in inertial coordinates. The stabilization of the aircraft may be accomplished through the use of an autopilot of one of the types in current use, but experience in this lart shows that it is dilicult to prevent small motions of an aircraft due to air motions, even with a 'good autopilot. Itis also possible to stabilize the antenna base against motion of the aircraft `by a servomecha-nism which operates to correct the orientation of the antenna base through reference to a gyro or other instrument which determines small rotations. In the case of the radar antenna conceived in connection with this instrument, such a mounting is difIicult to design Yand heavy and expensive to build. The antenna must be of large size and possess a large moment of inertia, so that a stabilization system which would keep it motionless with respect to the air frame in inertial coordinates with rapid response to error would have to be large and powerful to make the necessary corrections. It would also be necessary to make certain parts of the antenna stronger and make the mounting larger to provide for the necessary motion.

V'Consideration of .Figure 3 will show the geometry for the correction problem and indicate the Way in which it can be solved by inserting appropriate correcting signals in the computers and drive unit of the map printer to correct for small deviations ofthe aircraft from its'assigned angles of flight. Axes IA, 2A, and 'IA of Figure'S are an irrotational set of axes which travel with the aircraft. The aircraft is normally directed along axis IA, :and axis 2A is vertical. At the instant under discussion, however, the aircraft deviates from the axes by yaw angle a, pitch angle b, and roll angle c, which are taken as shown so that its momentary axes `are IA', 2A', and 'IA'. In the uncorrected system, no notice could be taken of thedeviation, and instead of path 4A' and printing the correct information as referred to terrain point '-SA, .the .uncorrected system would print data taken from the terrain at 6A', as though it had :been taken from position BA and would thus introduce ,distortion into the map in range, azimuth and elevation. The correction system'to be vdescribed below will work on the assumption that-the angles a, b, and c can be held downto a few degrees: so that cross interaction terms may be ignored. In the rectangular coordinate system of the aircraft, the correction is difficult to compute, but a transformation to a coordinate system which rotates with the radar antenna `simplifies the problem considerably.

The problem-of correcting the printing computation so that the printed data corresponds to point 6A instead of point -EA is that of computing angular correction p and applying it to the drive unit ofthe printer, radius correction q, and altitude correction m as shown on Figure 3.

In .terms Vof the roll, pitch, and yaw signals which.

may be derived from the aircraft autopilot system or from a pair of suitable gyroscopes, the transformed angles -are given approximately by the following equations: .Y Y

pra-I-ccos g5-b sings 7 e=b cos p-I-c sin qi 3 These equations Vmay be verified reasily by differentiation of the dening equations for 1), 1", and A and substitution of the values given in Equations 7 and 8 for the differential angles.

Figure 4 ,shows some of the details of the computing arrangement for correcting Athe printing computers. Vertical gyroscope ISI `may be a part of the aircraft autopilot, or it may be especially installed for the mapping equipment. It positions piclzoff elements |912 Vand |93 so that they produce alternating voltages at some constant frequency of phase and magnitude characteristic of angleof roll c and angle of lpitch b. Directional gyroscope |94 is equipped with pickoff element |95 which gives an alternating voltage output which varies similarly with yaw angle a.

The outputs of pickoffs |92 and |93 vare applied to the stator windings of resolvers 20| land 202 for the computation of the angular corrections. Radar antenna .|0| vis connected mechanically to resolvers 20| and 202 so that as it goes around in its search motion the ,rotors of the two resolvers revolve synchronously with it. The rotor windings of resolver 20| .thus pick upa Voltage proportional toc cos p-b sin o, and the windings of 4the rotor of lresolver 202 pick up a `voltage proportional to b cos Ic sin qs. The output voltage of resolver 20| is added algebraically to the voutput voltage lof pickoff element |95, which is proportional -to a-to generate the complete correctingterm for theangle qi. Selsyn transformer 203 operates synchronously with the rotation of radar antenna 0|. Selsyn differential generator 2i il is positioned by servomotor 2 3v in Aaccordance with the correction signal to .add the correction angle tothe output of selsyn 203 for transmission tomechanical drive unit The correction signal, p is usedas an input voltage to servoampliiier 2H whichdrives servomotor 2|3 so that selsyn diiferential 2|liis rotated to the correction angle, and followup unity 2| 2 generatesa signal equal and opposite-.to.thecorrecting signal and so stops the servomotor.

When the correction ksystem is used, the antenna |0| is driven by motor |02 of any desired type. This motor |02 drives selsyn transformer- 2&3 which generates a three phase alternating current of a frequency that varies in a direct straight-line proportion to the speed of motor |02. The ,phase of that alternating current is modied byselsyn differential 2|4 as has been'stated. The outputof selsyn differentiall M drives motors ll fandIlA whichin this case --are selsyn motors.,

Correction of the radius computation and the elevation computation for angular motion of the aircraft is carried out in radius computer I2 and in elevation computer II by varying the frequencies of the timing oscillators in these two units to take account of variations in the angle 0. The output of resolver 202 is applied to attenuators 2I5 and 2|6. Attenuator 2|5 is adjusted to multiply the voltage by sin 0, and this correction voltage is applied to oscillator |23 of radius computer I2 to modify its frequency. As shown in equation 5 for the uncorrected case, the frequency of this oscillator is =C cos /2 dr 5 Where C is the velocity of radar waves, and dlr is the smallest range difference to be distinguished. The effect of rotation of the aircraft which modifies 0 is to change this frequency to f=;(cos 0|sin @(b cos qS-i-c sin l2 Oscillator |23 is a vacuum tube os-cillator equipped with a reactance tube frequency modulator 2A25 or a servo operated variable condenser which changes the frequency linearly in accordance with the correction voltage selected above and thus corrects the radius computation. In order to -control oscillator |23, the wire 2| 5A of attenuator 2|5 (Fig. 4) is connected to wire 2I5A of oscillator |23 (see Fig. 6), with a suitable rectifier in between to convert the alternating voltage to a direct voltage.

The output of resolver 202 is modied in attenuator 2|6 by the cosine of 0 and passed to the elevation computer, where it modifies the frequency of oscillator II2 in a manner similar to that outlined above for the radius computer. The frequency equation in this case is r=2-dC-A (sin H-cos 0(b cos |c sin 115)) 13 where dA is the smallest altitude interval, and the other symbols have the same meanings as before. In order to control oscillator |I2, the wire 2|6A of attenuator 2||5 is connected to the wire 2I6A of oscillator I I2 of Figure 7.

I hereinabove discussed a type of automatic printer for use with an airborne radar set which would prepare contour maps or other types of maps indicating the relative elevations of the terrain over which the aircraft iiies. The following description outlines alternative forms of the same device, using some of the previous components, but providing for a considerable simplilication in the overall equipment. In the previous form of invention the maps were printed directly on facsimile paper. In this one, they are deposited as a latent image on photographic film or paper which must be developed subsequently. Although the device described here does not produce immediately useful maps, it has the advantage of reduced size and weight. The stabilization provided in the other case may also be provided here.

Figure 5 illustrates the general connectionsthe distance tothe element from the aircraft. The amplitude of the returned signal is an indication of the radar reflectance of the element under observation.

In this form of the device, drive unit |1C is used to move the mechanical parts 0f printers in synchronism with the antenna motion. It also moves a mechanical part 22a of elevation computer 22. Shaft 51C drives pinions I1D, ITE and I1F which respectively drive coil supports 1G and I'II-I and antenna IOI. 'I'his new type of elevation computer and new types of printer 20 and 2| are substituted for printers I5 and I6, radius computer I2, and selectors I3 and III and elevation computer I I of the previous form of invention. In operation, the trigger pulse from radar set I0, which originates at the time of pulse transmission from antenna IOI is sent on cable |02 to contour printer 20 and to elevation computer 22. The returned signal is sent on cable |03 to elevation computer 22 and to terrain echo printer 2|. Altimeter I8 serves to correct elevation computer 22, and the output of this latter circuit is applied to contour printer 20 for the production of a contour map on the iilm.

The operations of printer 20 in producing a contour map in the film image will now be described. Unexposed lm is drawn from supply roll 20| through the printer at a speed proportional to the aircraft ground speed by sprocket wheel 200, driven by motor 202. The exposed lm is stored on take-up reel 203 after passing through the printer. The focused spot of elec tron -current on the face of cathode ray tube 206 is caused to move radially by means of a fluctuating current in sweep generator 208 applied through deilecting coil 201. Deflecting coil 201 is turned mechanically to follow the motion of antenna II by drive unit |1C so that the radial trace on the face of cathode ray tube 206 follows the horizontal projection of radar beam 4. On the scale of the indicator tube, the spot is caused to sweep radially at a velocity equal to c sin@ where c is the velocity of light, and 0 is the angle of depression of radar beam 0 below the horizontal.

The lbeam of electrons which excites the phosphor of the cathode ray tube is controlled in intensity by the signal from elevation computer 22 and the light from tube 205 is focused by lens 205 in such a way that identifiable contour lines, or other significant elevation marks are made on the film at appropriate scale positions to indicate the elevation of the terrain elements observed. 'Ihe action of rotation deflection coil 201 and sweep generator 20S serve to locate the plotted points correctly in azimuth and in range, and the modulation from elevation computer 22 indicates the correct elevation data for the completion of the map.

Printer 2| is similar in every way vto printer 20, and it derives its sweep voltage from sweep generator 200. The intensity of the electron spot in the cathode ray tube of printer 2| is controlled by the intensity of the returned echo signal from the terrain rather than from an elevation computer. Printer 2| thus produces a map which is identical in scale and in distortions with that produced by printer 2S, but it contains terrain reflectance data rather than contour data.

I will now describe elevation computer 22. The xtrigger pulse from radar set I0 starts the action accents of delay circuit 228. This circuit introduces a delay period dependent on thereading-lof-altimeter i8 and then triggersthe operations ofsweep generator 222, which produces asawtooth waveform, pulling the spot of electron impact 'rapidly from top to bottom of cathode ray'tube' 22| and then permitting it to risefat a-'predeter'mined rate. VThe intensity grid of cathode rayrtube`22i is activated by the returned echo-'signal from radar set lil. The electron current to the face of tube 22 is-normally cut off, but when the echol signal from the terrain is received, a pulse of current is allowed to -vpass through tube 22 l making a bright spot on the face. The posi; tion in which the spot is made is determined by the aircraft altimeter I8, operating through delay circuit 228 and the elevation of v the'ter'rainelement from which the signal was reflected. The altimeter I8 is arrangedso that echoes from ter'- rain elements a given distance above'the selected base level are always recorded at one position on the tube face,falthough theaircraft--may 'iiyat any desired' altitude." 'The' altitude return-=from the face of tube' 225 is focussed by len's223 onto code wheel 22d. This wheelcomprises a transparentdiscwith a series offconcentric'codea rings thereon.` The ring having the smallestidiameter is in line with the upper endv of the trace |on tube? 22| and the ring having the largestdn ameter 'is in line with the lower end' of the trace. Coding is'accomplished by providing alternate opaque and transparent spots along the rings. Each ring is uniformly coded with diiferent rings differently coded. For example the..innermost ring is coded withV long dashes andv shortzspaces therebetween whereas the next ring is-fcodedwith short dashes andv long spaces. IThe ycode wheel is rotatedk m'echanically'by drive unit: iiC so as to remain in synchronisrn with theirotation of antenna IBI. The light which passesv through codewheel 224 isl condensed byfvlensfsystemrZZ onto the cathode of photocell22. The 'output signal of photocellx22 is amplified byampliner 221 and passed-to yprinter-:2lifor:contourr'line printing, or other type of elevation indication. The nature of the printing signal and therefore the type of elevation indication given in printer 20 is determined by the-manner in which light is allowedto pass through code wheel.. 224..,.Clontour lines may be achieved without rotating. the wheel by having a light screen with alternate sections opaque and transparent. Ii it is desired to identify. the individual contour lines, the wgheel may be rotated as indicated and each line may be interruptedv in a way which will identify it. If it is desired to print the various elevations as variations of density,.rather than 'as` countoui` intervals, code wheelv 224i may .be replaced by a density screenwhose density varies in the` desired way from top to bottom to pass the desired amount of light through to photocell 22B. .if it is `desired to print the map in a number of colors, wheel 224 may be replaced by a set of .small Alenses which will focus the light falling on themonto a number of separate photoc'ells,each correspending to a certain color inthe printer. The printer may be loaded with color nlm, and-three cathode ray tubes and lens systems: similar to tube 20e1 and lens 295 may be uSed'to--provide the three basic colors necessary to printing .colored bands to yindicate certain elevation levels. Figure 9 shows the parts of. elevation computer 22 and printer 2@ which would be involved in a system of color printing.

As shown in Figure 9, elevation computer 22,v

usescathode ray tube 221 to present the ground return isignal inY the'same way in which it was used; in the previous form. The altincter correction and lother features of the device arethe same. In-k this form, however, there are three lens systern's"223,v passing light from the cathode ray-'tube through three separate transmissionV screens 224` ,through three separate condensing lenses'225 and to three photocells 225. Three' amplifiers 22'1 pass the signals from the photo cells to the three cathode ray tubes 25S of rinter' 2U. Colors for printing in printer 2li are generated bythe Vthree color separation process well known to those skilled in color mixing, painting, or printing. The desired coloron the nlm map to correspond to a particular elevation is formed by thej mixing of Ilight of three separate colors from cathode ray tubes 2636A, ieEB and Theratio in-whiclr the three colors are mixed to denote any particular elevation is determined by the ratios of light transmitted b' correspon-:l-

ing steps of the three transmission screens in computer 22,. For a. given elevation, there is a given'position of the reiected terrain spot on the face` of cathode ray tube 22l. This spot position corresponds to a given position on each of transmission screens 22d, and the relative amounts of light received byf'photocells 22d are determined by'the relative densities of screens 225i. By appropriate choice of screens, it is possible to make any color range in the nished film correspond to any altitude range `which is desired. Although the color system has some complications not pres-V ent in the previous system, it has some advantages inv that'the'map it produces is more immediatelyuseful for some purposes.

"The systems ofFigures 5 and 9 as so far described are corrected for variations in altitude of the mapping aircraft but are not corrected for distortions in the map due to pitch, roll, or yaw of the aircraft. The correcting system described in the previous 4description can readily be applied to this system. ln this case it will be necessary asV before to provide corrected azimuth to drive unit" I'FC by means of the system shown in Figu're4 ofI theprevious description. The outputs of the-correcting system which served to correct radius and elevation operations are in thiscase appliedA to the sweep generators in the computers to modify the sweep rate in accord with the corrected depression angle of the radar beam. The radius correcting voltage would thus be usedY to modify the rate of sweep in sweep generator 2% and-the elevation correction voltage would be used to modify the rate of sweep from sweep generator222. According to the equations of operation of the system, the sweep rate required in sweep generator 222 is proportional to the sine of the 4depression angle of the radar beam below the horizontal plane. Figure l0 is a schematic diagram of a circuit which may be used in sweep generator-222 for the purpose'of producing the sweep waveformrequired and for the purpose of correcting this sweep rate. lt operates as follows. At the receipt of the synchronizing signal from delay circuit 228, condenser 2228 is momentarily charged by the signal in such a senseY as-to start the discharge of current in gas tube 2225. The current flowing in gas tube 22255 is limited by resistor 222%. rThe current serves to charge condenser 2224, and as the voltage on condenser 2224 approaches the supply voltage, the current diminishes, and the Vdischarge in gas tube 2225 is extinguished. Once the discharge is extinguishe'd,V the high positive potential of the cathode with respect to the grid of tube 2225 serves to maintain the tube in a non-conducting condition until the discharge is once more initiated by the positive synchronizing pulse. As soon as condenser 2225i is charged to a positive potential, the charge starts to leak off through vacuum tube 222|. Tube 222| is of the ve electrode type and is so constructed that the current through the tube is dependent on the voltage between grid and cathode to a much greater extent than on the voltage between cathode and plate. In normal operation, the voltage from grid to cathode is provided by the voltage drop through resistor 2222 of the plate current of the tube. This has a stabilizing effect on the tube current and causes the tube to draw a constant current from condenser 22d and thus to diminish the voltage across condenser 22M at a constant rate and to produce a sweep voltage which Varies linearly with time. The rate of this linear variation may be changed and corrected in this sweep circuit by the addition of an appropriate voltage in the grid circuit of tube 222|. In the corrected version of the computer, the computed change in the depression angle of the radar beam is multiplied by the cosine of the depression angle and applied as a voltage to the grid of tube 222| to correct the rate of sweep of the electron spot on the face of cathode ray tube 22|. A similar sweep generator is used in the radius presentation in printer 20.

It is understood in connection with Figure that by suitable modification the contour printer 20 and the terrain printer 2| may be combined to print upon a single nlm. This can be done -i either by (a) using the two cathode ray tubes of the two systems arranged that they sweep the same trace upon the same nlm or (b) by omitting the terrain printer and adding its grid (still connected to wire |63) to cathode ray tube 20B.

I claim to have invented:

l. In an airborne map printing system, radio means for detecting objects of terrain, means responsive to the output of said radio means to print a map of the objects of terrain, said lastnamed means including printing means for printing the map, additional means responsive to the output of the radio means for separately printing contour lines of the terrain, said additional means including printing means for printing contour lines, and means for synchronizing the two printing means so that contour lines as printed by the second printer are the contour lines of the terrain printed by the first printer.

2. In an airborne map printing system., means for making a map of the terrain adjacent the path of ilight of the aircraft, means for simultaneously making an additional map of said terrain which consists of spaced continuous lines i:

each of which lines represents an imaginary line on said terrain all of the points of which are at the same elevation, said last-named means including means for making its map to the same scale as the map produced by the first-named means, and means for synchronizing the operations of the rst and second named means so that the lines on the second map are those applicable to and constituting contour lines of the terrain indicated on the first map.

3. In a radio detection system for aircraft; means for scanning the terrain in a predetermined manner comprising an airborne pulse modulated radio transmitter for radiating toward the ground, and receiving means for detecting return reflected waves of the carrier frequency of the transmitter; signal generating means responsive to the time difference between the outgoing and return waves for modifying its signal when such time diiference conforms to one of several predetermined values; and indicating means synchronized with said scanning means and which when actuated produces indicia which conforms to the position being scanned by the scanning means at the instant of such actuation; said signal producing means including means to apply its signal output to said indicating means to actuate the same by the modifications of its signal output, the system including means for modulating the output of the signal generating means in different ways respectively when the said time difference conforms to different ones of said several predetermined values, said indicating means including means for giving different indications respectively in response to different modulations of the signal generating means, said system including in addition an altimeter for determining the absolute altitude of the aircraft and means responsive to variations of said altimeter for selecting said predetermined values according to the reading of said altimeter and includes means to provide large predetermined values when the aircraft is at a high level and lower predetermined values when the aircraft is at a low level, to thereby compensate for variations in the altitude of the aircraft.

4. In an airborne radio terrain map printing system, radio terrain scanning means including a pulse modulated radio transmitter and a receiver for receiving returned waves from the terrain, said scanning means including a rotating part for causing the scanning to take place in a circular path the center point of which path is directly below the aircraft, signal producing means responsive to the time difference between the outgoing and reflected pulses for modifying its signal output according to the duration of such time difference, said signal producing means including means for modifying its signal output only when such time diiference conforms to one cf a series of time difference values and also including means for producing different modulations of its signal output for different difference values of said series, printing means for forming distinctive indicia respectively in response to the different ones of said modulated signal outputs, means for moving the surface to be printed past said printing means at a speed proportional to the ground speed of the aircraft, and means for I varying the angle at which printing is eiected by the printing means synchronously with said rotating part.

5. In a system for printing contour lines, a cathode ray tube having a screen, a strip of photographic film exposed to the screen of said tube, means for moving said lm parallel to the face of said screen at a speed proportional to the ground speed of the aircraft, a rotating directional antenna on said aircraft for directing signais toward and receiving signals from a conned spot of terrain, means for directing the antenna at a fixed angle to the vertical and for rotating the same in a circular path about a vertical aXis, cathode ray defiecting means associated with said tube for rotating the beam of cathode rays synchronously with rotation of said antenna, radio transmitting and receiving means connected to the antenna for transmitting an outgoing pulse of radio frequency energy and receiving any return reflected pulse due thereto, a

for deiiecting its trace along a linear path, a sawvtooth sweep generator connected to the lastnamed ,deflectingmeana control means responsive to transmitted pulses for` starting the sawtooth sweep of said sweep generator, said second tubehaving an intensity grid means for energizing said intensity grid by received reflected pulses, and light-responsive means responsive to the position of any intense spots on the trace of saidsecond tube to intensity modulate the rst tube, said last-named means including annintensity grid Afor the first tube and means for energizing the same only when intense spots appear on the screen of the rst tube at predeter- Ininedpoints thereon.

6. The lsystem of claim in which said light responsive means comprises a series of dilerent light transmitting elements located in front of theV second tube and so that the light transmitted by that tube at dilerent positions along the linear trace is Vaiected indifferent ways, said lightresponsive means also including means responsive to the light passedthrough said elements for controlling the intensity grid of the` rstgrid to anextent distinctive of the way the light passingthrough said elements was aiected thereby.

'7. The system dened in lclaim 5 in Vwhich the light responsive means comprisesthe combination of a code wheel and a light-sensitive cell, said code wheel having `a plurality of concentric rings each o1" which ringshas a differentV series oi distinctive markings, said rings being spaced from each other andV located immediately in front of said linear trace so that the radius of v,

the vcode, wheel` is parallel to and adjacent the linear trace and so that any light spots on the trace will be concentrated upon a part of the radiusiof the codewheel, said cell being responsive to light transmitted fromthe cell through the code wheel, the cell output being connected tor control the intensity grid of said rst tube, and means forrotating said code wheel.

8.,The system denedin claim 5 in which the controlmeans is a delay circuit which starts the saw-tooth sweep only after a time interval following the transmission of the outgoing pulse, and an altimeter for varying the delay eiected by the delay circuit to increase the delay when the aircraft isV ascending and to decrease the delay when the aircraft Yis descending.

9. Inan airborne devicefor printing different contour lines indifferent colors, a plurality of cathode ray tubes each having means cooperating therewith to produce adifierent color than those produced by the others, a strip of photographic color film exposed to all of said tubesnso that spots `of light in complementary places on the several tubes will coincide on the nlm, means for movingY said film relative to said tubes at a speed proportional to the ground speed of the aircraft, arotating,directional antenna on the aircraft for directing signals toward and receiving signal's from a confined spot of terrain, means for directing the antenna at a fixed angle to the vertical and for rotating the same in a circular path about a vertical axis, cathode ray deflecting means associated with each of said tubes, means for rotating each of said cathode ray deflecting means in synchronism with rotation of said antenna, radio transmitting and receiving means connected to said antenna for transmitting an outgoing pulse of radio frequency energy and receiving any reflected return pulses, a saw-toothsweep generator connected to said deflecting means, means responsive to each outgoing pulse to triggerthe saw-tooth sweep generator into operation, another cathode ray tube having a dei'iecting element for moving the trace thereof along a predetermined path, a sawtcoth sweep generator for energizing the lastnamed deflecting element, means responsive to each outgoing pulse to trigger the last-named sweep generator, said other cathode ray tubeV including an intensity grid, means to energizesaid intensity grid by return pulses, a plurality of light screens oneV for each of said plurality of cathode ray tubes, said light screens being respectively mounted in paths of light leavingsaid other cathode ray tube and varying in transparency along the same separate light-sensitive cells respectively responsive to the respective light rays passing through said screens, each of said plurality of cathode ray tubes havingr an intensity grid, and means respectively connecting said cells` ings vary, said signal producing devices including means varying their signal outputs according to different mathematical laws as the said spacing varies, a plurality of light producing means for respectively producing light rays of different colors, there being one of said light producing means for each signal producing device and each light producing means including means for varying the intensity of the light output therefrom according to variations in the output signal of its complementary signal producing-device, means for moving the light output kof the light producing means to positions corresponding to the position of the terrain being examined by the elevation-responsive means, a strip of color film, and means for condensing the light outputs from the plurality of light producing means onto the film with the light outputs of all of the light producing means always forming coincident spots on the film.

11. In a system for printing contour lines, a rotating directional antenna, a radio transmitter feeding its output to said antenna, a radio receiver receiving waves intercepting the antenna, a pulser for modulating the transmitter, delay circuit energized by the pulser, first oscillator actuated by the output of the delay circuit which begins its oscillations when so actuated, a plurality of elements respectively energized by suecessive pulses from the oscillator, a second oscillator, means connected to the pulser for starting the second oscillator to oscillate. a coincidence circuit responsive to the output of the second oscillator and also responsive to the output of said receiver to pass a pulse when concurrently energized by the second oscillator and the receiver, modulating means for modulating the output of the coincidence circuit, said modulating means including means to vary the amplitude of its output depending on the number of pulses produced by the second oscillator', a plurality of plementary element and by the modulating means, a plurality of concentric conducting rings insulated from each other, a sheet of chemically treated paper which changes its color when electric current ows therethrough, means for moving said sheet across the edges of said rings, an electrode pressing on the side of the paper opposite that which touches said rings, and means for rotating said antenna and said electrode synchronously with the electrode rotating about the center of curvature of said concentric rings, said delay circuit and said first oscillator having such interrelationship that the output pulses from the oscillator will occur at times which are respectively proportional to the several radii of the concentric rings.

12. In an airborne terrain elevation determining system, an altimeter for determining the absolute altitude of the aircraft above a base plane of known altitude which vplane is at an altitude diierent from that of said terrain, radio means for determining the vertical height of the aircraft above the terrain, and means responsive to the difference in the determinations of the absolute altimeter and the radio means for indicating the altitude of the terrain.

13. In an airborne terrain elevation determining system, radio means for determining the distance from the aircraft to the terrain along a line which is at an acute angle to a vertical axis that passes through the aircraft, altitude indicating means responsive to the output of the radio means, means to compensate the altitude indicating means for the error introduced due to the angle of measurement of the distance so that it indicates the altitude of the aircraft above the terrain, altitude determining means for determining the altitude of the aircraft above a known datum plane, and means for modifying the indicating means according to the output ci' the altitude determining means, said indicating means including means responsive to the altitude determining means and the radio means for indicating the altitude of the terrain.

14. In an airborne map printing system, radio means for detecting objects of terrain, means responsive to the output of said radio means to print a map of the objects of terrain, said lastnamed means including printing means for printing the map, additional means responsive to the output of the radio means for separately printing indicia indicative of the contour of the terrain, said additional means including printing means for printing said indicia, and means for synchronizing the two printing means.

15. A map printing system comprising a printer; said printer comprising a plurality of concentric conducting rings which are insulated from each other, means for moving one face of a sheet of material on which printing is to be effected across the face of said concentric rings, and a printing element pivoted for rotation about the axis of said rings and movable relative to the other face of said sheet; a plurality of coincidence circuits, one for each of said rings and connected to its complementary ring; each coincidence circuit including two inputs and including means for modulating the current to its complementary ring in response to concurrent predetermined states oi the two inputs; a radio pulse detection system comprising a pulse modulated transmitter and a receiver; means for feeding the output of the receiver to one of the inputs of each of the coincidence circuits; and means synchronized with outgoing pulses of said transmitter for thereafter sequentially varying the energizations of the remaining inputs of said coin- 26 cidence circuits; said transmitter including a rotatable antenna; and means for synchronously rotating said antenna and printing element.

16. A map printing system comprising a plurality of concentric rings composed of conducting material and insulated from each other, means for moving one face of a sheet of material across one face of said rings, a rotatable conducting printing element pivoted coaxial with said rings and movable across the other face of said sheet, a plurality of coincidence circuits one for each ring, each coincidence circuit including two input circuits and means responsive to predetermined ccncurrent energizations of said inputs for passing a current from the coincidence circuit to its complementary ring then through said sheet and to said printing element, a pulse modulated transmitter and a complementary receiver, said transmitter and receiver including rotatable antenna means, means for synchronously rotating said antenna means and said printing element, means for feeding the output of said receiver to one of the inputs of each of the coincidence circuits, and a circuit for energizing the other inputs of the coincidence circuits sequentially between transmitted pulses.

17. An airborne map printer as defined in claim 16 in which said means for moving the sheet of material includes means for moving the material at a speed proportional to the ground speed of the aircraft.

18. An airborne map printer' as defined in claim 17 in which the means for feeding the output of said receiver` to one of the inputs of each of the coincidence circuits comprises elevation computing means which passes received impulses only when they occur at one of a series of predetermined time displacements away from the transmission of an outgoing pulse.

19. A map indicating system comprising indieating means having a plurality of discrete elements whi-ch elements are respectively capable of producing indications at successive points, a plurality of coincidence circuits one for each of said elements, each coincidence circuit including two inputs and also means for controlling its complementary element to give an indication in response to the occurrence of predetermined states on its two inputs, a pulsed transmitter, a receiver for reected Waves that originated at said transmitter, means feeding the output of said receiver to one input 'of each of said coincidence circuits, and means for sequentially energizing the other inputs of said coincidence circuits between outgoing pulses.

20. An airborne map printing system for printing both a map of the terrain and a contour map comprising in combination a pulse modulated transmitter, a receiver for receiving waves from said transmitter reflected by the terrain, an antenna for the transmitter and receiver, a plurality cf concentric rings composed of conducting material and insulated from each other, means for moving one face of a sheet of material across one face of said rings, a rotatable printer of conducting material movable across the other face of said sheet, a second plurality of concentric rings composed of conducting material and insulated from each other, second means for moving one face of al second sheet of material across one face of the second plurality of rings, a second rotatable printer of conducting material movable across the other face of the second sheet of material, means for synchronously rotating the antenna and said printers, a coincidence circuit -with thering and then to they printer touching -jtfhesheet means for energizing onev of the inputs of each of the coincidence circuitsvassociated with thesrst plurality of rings whenever a pulse is -,f'received-.on saidireceiver, means for energizing saoneof the inputs of each of the coincidence circuits associated with the second plurality of rings #whenever `a pulse isreceived at the receiver at fanyof a series of equally spaced time intervals ffollowi-ngathe transmission of a pulse, and means ffor ,senqilerit-iallyv energizing the remaining inputs of the rstfas-Awell as ofthe second group of coin- M. cidence ycircuits following each transmitted pulse y--With vspaced time intervals-between successive fenergizations of a diierent and shorter order than the irstenamed time intervals.

4,21. vThe systemzof claim 12 in Which the radio rneans, comprises a pulse echo system including a z-altimeter to reduce .the indicated time displacelfrnentof echa-pulses as compared to outgoing pulses as the absolute altitude of the aircraft ,l

increases.

RICHARD C. RAYMOND.

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